This invention relates generally to semiconductor devices and manufacturing processes, and more particularly, the invention relates to such devices fabricated in silicon on insulator (SOI) structures.
Reduced parasitic components can be achieved in semiconductor devices by fabrication of the devices in a silicon on insulator structure, such as silicon on sapphire and silicon on oxide insulator, including commercially available bonded silicon on insulator and implanted oxide (SIMOX). In such structures the supporting substrate is typically bonded to a heat sink for heat removal, which is particularly important for power transistor structures. Additionally, a ground plane can be provided by metallization on the substrate surface.
The present invention is directed to an improved method of fabricating silicon on insulator structures with improved heat removal and circuit ground configurations including low resistance ground paths.
In accordance with the invention a semiconductor device is fabricated in a silicon on insulator (SOI) substrate including a supporting silicon substrate, a silicon oxide layer supported by the substrate, and a silicon layer over the silicon oxide layer. More particularly, an electrical component such as a transistor or capacitor, for example, is fabricated in the silicon layer over a portion of the silicon oxide layer, and then the portion of the substrate opposite from the component is masked and etched. A metal layer is then formed in the portion of the substrate which has been removed by etching with the metal layer providing heat removal from the component. In an alternative embodiment, the silicon oxide layer overlying the portion of the substrate is removed with the metal layer abutting the silicon layer.
In fabricating the device, preferential etching can be employed to remove the silicon in the substrate with the silicon oxide functioning as an etchant stop. A two step etch can be applied, also, with the last etch being preferential. The exposed silicon oxide can then be removed, as in the alternative embodiment, by preferential etchant of silicon oxide.
A hard mask of silicon nitride, for example, can be formed on a surface of the substrate for the silicon etching. Infra red mask alignment or mirror alignment can be employed in masking and etching the silicon nitride in forming the hard mask. The metal layer preferably comprises a refractory metal covered by gold. Wafer abrasion can be employed to thin the substrate prior to masking and etching.
The invention and objects and features thereof will be more readily apparent when the following detailed description and appended claims when taken with drawings.